Masonry units, sometimes referred to as concrete masonry units (CMUs), include segmental retaining wall (SRW) units, pavers, and architectural blocks, all of which are made from a "masonry concrete" which is comprised of hydratable cement binder and fine aggregate (e.g., particles of which less than 5% have a diameter greater than 0.375 inch). Masonry concrete lacks the coarse aggregate (typically greater than 0.5 inch diameter) that is further used in conventional concrete, such as, for example, ready-mix concrete.
More significantly, masonry concrete differs from conventional concrete because it is said to have zero "slump," or, to employ a more accurate definition, it is said to have a practically immeasurable fluidity. The slump property is determined by placing wet masonry concrete into an inverted cone and then removing the cone, and measuring the distance (if any) by which the cone-molded sample drops in height. See ASTM C143 (1988) ("Standard Test Method for Slump of Portland Cement Concrete"). Typically, the slump of masonry concrete is 0-0.75 inches, and thus masonry concrete is said to have an essentially "zero slump."
The present inventors believe that the use of fatty acid-based efflorescence control admixtures (ECAs), which are sometimes referred to as integral water repellants, such as calcium stearate dispersion, fatty acids and their salts and esters, etc., can cause an appreciable loss of freeze-thaw durability in masonry units (e.g., made of zero slump masonry concrete). Efflorescence is the appearance of white, patchy stains on the face of masonry units during their manufacture or after their installation in the field. Once installed in the field, the masonry blocks are subjected to routine weathering conditions, one of them being alternate freezing and thawing (F/T) cycles. Recent testing of F/T durability of masonry units (SRW), using the ASTM C1262 (1995) test method in the lab, revealed severe adverse effects of ECAs on the F/T durability of masonry units.
Accordingly, an improved masonry concrete admixture, masonry concrete having improved freeze/thaw durability, and methods for making these, are urgently needed.